1. Field of the Invention
The present invention relates to a heat radiation system for electric circuitry.
More specifically, the invention relates to a heat radiation system for electric circuitry including a "solid body releasing heat in balance, as it has a higher temperature than a surrounding body" (hereafter called "solid heat source body" or simply "heat source"), a "solid body receiving heat in balance, as it has a lower temperature than the heat source" (hereafter called "solid heat sink body" or simply "heat sink"), and a "body of medium or media conducting heat in balance in between, as it has a gradient or gradients of temperature continuously descending from the heat source to the heat sink" (hereafter called "heat conducting circuit" or simply "heat circuit").
In particular, the invention is associated with electric circuitry having a "positive temperature coefficient thermistor" (hereafter called "PTC device"), and a heat radiation plate for the PTC device.
2. Description of Relevant Art
The PTC device is installed in an electric circuit connected to an electric load. The circuit conducts an electric current, which generates Joule's heat at "a positive temperature coefficient resistor element" (hereafter called "PTC element") of the PTC device, whereby the PTC element is heated and has a temperature in accordance with an occasional heat balance. If the temperature exceeds a specified level, the PTC element trips to have a suddenly increased resistance so that the current is interrupted.
To restore the PTC element, its temperature needs to be lowered by dissipating heat through a heat radiation mechanism, in which the PTC element and electrodes in contact therewith release heat and one or more forced or natural heat-radiation members and large heat-capacity structural members near the PTC element receives heat.
A known PTC element comprises a body of thermally sensitive polymer and a system of electrically conductive particles suspended therein, and the body of polymer is adapted for a significant thermal expansion to have a decreased density of conductive particles to provide an increased resistance. A PTC device with such a PTC element is sometimes employed for electric or electronic control in an automobile.
Conventional techniques for radiating heat from a PTC device have been the provision of a metallic enclosure or wall with or without fins, see Japanese Patent Application Laid-Open Publication No. 4-78104, published Mar. 12, 1992, Japanese Patent Application Laid-Open Publication No. 61-234502, published Oct. 18, 1986, Japanese Utility Model Application Laid-Open Publication No. 62-163902, published Oct. 17, 1987, and Japanese Patent Publication No. 2-41161, published Sep. 14, 1990.